1. Field of the Invention
This invention relates to a sealing assembly particularly to be used in combination with a manhole cover to facilitate a fluid tight seal between the inner surface of the cover and the mounting ring surrounding the manhole on which the cover rests. Cooperatively configured and dimensioned groove and gasket structures are carried by the cover to facilitate an efficient seal and a long lasting and reliable sealing assembly to accomplish such seal.
2. Description of the Prior Art
The use of covers for the closing and covering of manholes is, of course, common practice. It has been found, however, that rain water or other occumulated ground water can enter the hole through vents or apertures purposely formed in the manhole cover for purposes of venting gasses or for purposes of removing the manhole from its covering position relative to the hole. In addition, rain water can enter around the edge of a manhole cover and enter the sewer, because many manhole covers are not equipped with any type of peripheral inner surface sealing structure. Without such a sealing structure or facility associated with the manhole cover the surface to surface contact usually is not sufficiently water proofed to prevent the entry of such rain water. This is particularly true if the manhole cover and cover frame have been in service for some time resulting in imperfections or inconsistencies in the mating surfaces.
In an attempt to overcome problems existing in the prior art of the type set forth above a sealing manhole cover for use on existing unsealed sanitary sewer manhole cover frames of the type disclosed in the U.S. Pat. No. 4,101,236 to Meyer, was devised. This structure relates to a sealing means in the form of an o-ring groove having a rectangular transverse configuration and dimensioned to receive an o-ring type gasket and having a depth slightly more then one half the thickness of the o-ring gasket and a width substantially equal to the width of the gasket such that the gasket is slightly compressively held in place in the groove with a portion of the gasket extending beyond the groove when the gasket is not compressed into its sealing position.
While operative for its intended function, the structure of the type disclosed in the above set forth patent includes certain recognized disadvantages as set forth in greater detail hereinafter.
If the sealing gasket is held in place by compression it is usually stretched, linearly to reduce the diameter thereof for easy installation into the holding groove. Friction on the sides of the groove prevents the gasket from going back to its original length. Over a period of time, portions of the gasket pull apart leaving a gap through which water can leak. This same stretching or linear expansion due to the resiliency of the material from which the gasket is formed, and normally applied to the gasket at the time of installation into the groove, if not uniform along its length, causes conventional gaskets to vary in diameter after placement into the interior of the groove. This means that the contact surface of the gasket is frequently not consistently flat along its length resulting in possible leak. In addition, gaskets which are held within the groove by compression, may not be seated in the bottom of the groove causing the contact surface of the gasket not to be flat. Other structures and practices prevalent in the prior art sometimes include the maintenance of the gasket within the groove using an adhesive or glue. Such use makes it impossible to replace a damaged gasket thereby necessitating extensive time for repair or replacement.
Accordingly, there is a need in this area for an improved sealing assembly for use in the environment as set forth above which provides proper sealing characteristics for an extended period of time and with an increased reliability.